A major problem for many years has been the development of a low power consumption, reciprocal and low loss microwave/millimeter-wave phase shifter. Microwave and millimeter-wave phase shifters are commonly realized in a ferrite based, anisotropic configuration or as a discrete switched line phase shifter configuration. Although some digital phase shifters exist at lower frequencies, such phase shifters do not directly apply at high microwave and millimeter-wave frequencies or would subsequently require some type of frequency translation circuits to realize the phase shifting affect. Additionally, the ferrite based units exhibit a hysteresis characteristic in the phase shift phenomena as a function of the bias current pulse. This hysteresis affect requires that two large bias current pulses, of several amps of peak current, be applied to the phase shifter. The magnitude of the bias pulse generally requires external high power, bias electronics. An alternative phase shifter is a transistor based, switched line phase shifter. Insertion loss is an issue, especially at millimeter-wave and high microwave frequencies. Fiber optic phase shifters are also employed but the extensive attenuation of the signal during translation requires substantial signal amplification making such an approach very costly; again this approach is non-reciprocal. Voltage variable dielectric ceramics, like barium strontium titanate, have been used but the thousands of volts required for biasing and the high insertion loss make this a poor choice.
Another problem has been the realization of a low cost, electronically scanned antenna (ESA) for applications that could not afford the cost and complexity of either a Transmit/Receive (T/R) module based active array or a ferrite-based phased array to achieve electronic beam scanning. These applications include low cost radars for un-manned air vehicles and communication systems, like point-to-multi-point communication systems.
Electronic scanning of a radiation beam pattern is generally achieved with either Transmit/Receive (T/R) module-based active arrays or ESAs that employ ferrite-based phased arrays. The phase shifter is behind each radiating element in the array. Both methods employ expensive components, expensive and complicated feeds and are difficult to assemble. Additionally, the bias electronics and associated beam steering computer are relatively complex. Other methods to achieve beam steering are the PIN diode based Rotman lens and the voltage variable dielectric lens. The latter employs barium strontium titanate (BST). BST is a voltage variable, dielectric material system to achieve the beam steering. Both require either high current or high voltage (10,000 volts) biasing requirements, as well as having a high insertion loss. The large insertion loss results in a low efficiency and low gain antenna and severely limits the practical application of these technologies for ESAs.
Another problem for many years has been the realization of a broadband standing wave antenna. Although the standing wave antenna is an efficient architecture, the frequency dependent nature of the short circuit termination of that antenna topology limits its usefulness.